This study examined the relationship between myofibrillar disruption and muscle protein synthetic rate (MPS) following an isolated bout of concentric (Con) or eccentric (Ecc) resistance exercise in six strength-trained males. MPS was calculated from the enrichment of L-[1,2-13C2]leucine in biopsies using the primed, constant infusion technique with the midpoint of the assessment period being approximately 24 h post-exercise. We conclude that the Ecc phase of resistance exercise is most disruptive to skeletal muscle, that training attenuates this effect, and that exercise-induced fiber disruption is essentially repaired after 5 d of inactivity in trained subjects.